In systems in which the current consumption is critical and, in addition, great power dynamics have to be processed, for example, in mobile radio systems, it is useful to switch off and bypass individual amplifier stages in RF (radio-frequency) amplifiers and/or amplifier chains. A dynamic range, for example, can be improved by this and an average current consumption can be reduced since appropriate amplifier stages can be switched off if necessary.
An example of this would be a reduction in the amplification in GSM (global system for mobile communication)/EDGE (enhanced data rates for GSM evolution) systems when, in switching, altering from GMSK (Gaussian minimum shift keying) modulation of a constant envelope to a 8-PSK (phase shift keying) modulation of a non-constant envelope. Whereas in GMSK, an amplifier can operate in the non-linear range of its amplification characteristic curve, this is no longer possible for 8-PSK, since information symbols here are not only encoded as to signal phase, but also as to signal amplitude (with symbol transitions). Another application example is a reduction in the current consumption in so-called low power modes in UMTS/3G systems.
Ways of reducing the amplification of an amplifier are, for example, wiring the amplifier and/or amplifier element, for example, a transistor, to negative feedback. In a bipolar transistor, this may, for example, be an emitter negative feedback or another feedback path in which a certain portion of the amplifier output power is returned to the amplifier input. In this manner, an amplification may be reduced, but there is no reduction in the current consumption.
Consequently, a bypass circuit that can reduce a current consumption in a bypass case and can be integrated in a common manufacturing process with the amplifier and/or amplifier element would be desirable for amplifier stages and/or amplifier elements.